The present invention relates to microprocessor-based electropneumatic type locomotive brake control systems and particularly to an improved brake pipe charging cut-off valve arrangement for such a locomotive brake control system.
Modern-day locomotive controls, including the locomotive brake control system, incorporate computer technology to reduce hardware and to facilitate adaptation of the system to various customer requirements.
In one such brake control system, described in U.S. Pat. No. 5,222,788, a cab-mounted, handle-operated, brake controller outputs a desired brake command signal to a microprocessor unit, which interprets this brake command signal in terms of a feedback signal indicative of the pressure of air in an equalizing reservoir, and then effects operation of application and release electropneumatic valves to adjust the equalizing reservoir pressure in accordance with the brake command signal.
A high-capacity pneumatic relay valve device is employed to vary the trainline brake pipe pressure in accordance with variations of the equalizing reservoir pressure, in order to control the railway car brakes. This so-called brake pipe control circuit of the aforementioned brake control system is shown and described in U.S. Pat. No. 4,904,027.
The brake control system further includes a locomotive brake cylinder control circuit having electropneumatic application and release valves. The locomotive brake cylinder control electropneumatic valves are operated by the microprocessor in response to changes in brake pipe pressure initiated by the brake pipe control circuit in accordance with movement of an automatic brake handle of the cab brake controller. Another high-capacity pneumatic relay valve device controls the pressure in the locomotive brake cylinders according to the pressure output of the locomotive brake cylinder control circuit application and release electropneumatic valves.
The electropneumatic valves in the brake pipe control circuit and in the locomotive brake cylinder control circuit are arranged to assume a pressure release state, in the event of a power loss at the microprocessor unit. In consequence of such a power loss, therefore, brake pipe pressure is reduced while, concurrently, the locomotive brake cylinder pressure is released. A pneumatic back-up control valve in the locomotive automatic brake control circuit is provided to establish locomotive brake cylinder pressure in response to the afore-mentioned reduction of brake pipe pressure resulting from such fail-safe operation of the electropneumatic valves in the brake pipe pressure control circuit, there being a double check valve to separate the pneumatic backup control valve from the electropneumatic valves in the locomotive brake cylinder control circuit.
Additional electropneumatic valves are employed in conjunction with a charging cut-off valve in a branch pipe via which the brake pipe pressure control circuit is connected to the locomotive brake pipe. The charging cut-off valve is provided to establish communication between the brake pipe pressure control circuit and the brake pipe when the locomotive is set up for "lead" operation, as a controlling locomotive, and to interrupt such communication when the locomotive is set up for "trail" operation, as a non-controlling locomotive.
The afore-mentioned charging cut-off valve is bistable and thus remains in its set position in the event of a microprocessor malfunction that causes a loss of power. In the event such a malfunction occurs on a controlling locomotive that is subsequently downgraded to non-controlling status, it will be appreciated that the charging cut-off valve remains in its previously set open position. Typically, such a non-controlling locomotive is hauled "dead", i.e., without electrical power, whereby the application and release electropneumatic valves in the brake pipe pressure control circuit are de-energized. This in turn causes the relay valve in this control circuit to assume an exhaust condition, thereby venting the brake pipe via the open charging cut-off valve. Accordingly, the ability to recharge the brake pipe from another controlling locomotive, following a "loss of power" brake application, could be jeopardized.